[llvm] [IR] Use SmallDenseSet in dropUnknownNonDebugMetadata (NFC) (PR #98853)

[Kazu Hirata via llvm-commits]

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@@ -1590,7 +1589,7 @@ void Instruction::dropUnknownNonDebugMetadata(ArrayRef<unsigned> KnownIDs) {
   if (!Value::hasMetadata())
     return; // Nothing to remove!
 
-  SmallSet<unsigned, 4> KnownSet;
+  SmallDenseSet<unsigned, 32> KnownSet;
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kazutakahirata wrote:

I measured the performance with rdtsc.  `SmallSet<unsigned, 32>` is about 1% faster than `SmallDenseSet<unsigned, 32>`.  I'm going back to `SmallSet`.

https://github.com/llvm/llvm-project/pull/98853